Various pacing methods such as “Search AV” and “Managed Ventricular Pacing®” are designed to promote intrinsic conduction of paced or intrinsic atrial events to the ventricle. Such methods are illustrated, for example, in U.S. Pat. Nos. 7,130,683 and 5,861,007, respectively entitled “Preferred ADI/R: A Permanent Pacing Mode to Eliminate Ventricular Pacing While Maintaining Back Support” and “Adaptive Search AV and Auto PVARP Adaptation to Same with Additional Benefit,” both of which are incorporated by reference in their entireties herein.
Clinically, such pacing methods may result in very long atrial-ventricular (AV) delays (e.g., longer than 300 ms). Such long AV delays may result in short ventricular—atrial (VA) intervals, depending on, for example, the heart rate, atrial pressure, duration of ventricular systole, and the rate and extent of ventricular relaxation. In some of these instances, the result may be atrial contraction against a closed mitral (or tricuspid) valve that results in increased atrial pressure and deceleration or frank reversal of pulmonary venous (or caval) flow. Thus, atrial function, ventricular filling (diastolic ventricular function), and ventricular systolic performance may be compromised under these circumstances.